The invention relates generally to computed radiography (CR) systems and more particularly to a system and method for improving the scan speed and image quality in computed radiography systems.
Computed radiography systems employ imaging techniques that capture X-rays as they pass through an object to be imaged using an imaging plate coated with a storage phosphor. The object to be imaged is typically exposed with X-rays, and a latent X-ray image is formed on the imaging plate. The storage phosphor on the imaging plate when stimulated with a low energy scanned light beam (such as a laser beam) releases visible light at locations where X-rays are absorbed. The light is then captured and converted into an electrical signal, which is subsequently converted to data that can be transmitted to remote systems or locations and displayed on laser-printed films or softcopy workstations and stored digitally.
Traditionally, computed radiography scanning techniques employ a continuously scanning laser beam with an optical integrating detector system. Scanning is typically performed in a raster format to cover the entire imaging plate. The scanning laser beam repeatedly scans the imaging plate in a horizontal direction while the imaging plate is slowly moved in an orthogonal direction thus scanning the entire plate surface. Some CR systems also employ a linear array scanner that scans the imaging plate one line at a time with a line of stimulating light. However, linear array CR scanners require that the scanning device transport the imaging plate past an optical read device (using a system of rollers). This contact may eventually damage the imaging plate to a point where it is no longer usable. The above scanning approaches limit the amount of light that can be collected from the storage phosphors as the residence time per pixel or per line is limited by a practical scan time taken for the imaging operation. In addition, calibrations of these devices are one-dimensional (one row across the plate) and do not compensate for non-uniformities in the X-ray beam or phosphor granularity.
In addition, and as will be appreciated by those skilled in the art, only a portion of the X-ray energy deposited onto the CR phosphor plate is generally stored. A substantial amount of light (due to the impinging X-ray energy) is emitted promptly at the time of exposure, which is generally not captured by a detector. Therefore, much of the energy deposited onto the CR plates is lost due to failure to collect this prompt emission. Further, in existing CR reading processes used to retrieve the stored emission information, some signal remains in the phosphor plate, which is typically wasted during the erasure cycle. The X-ray energy losses due to prompt and non-retrieved stored emission reduce the detective quantum efficiency and signal to noise ratio for X-ray exposures that would otherwise result in a much higher image scan quality. In medical applications, this energy is imparted to the patient without benefit of enhanced diagnosis. In nondestructive testing applications, this wasted energy results in longer throughput cycles for collecting imagery than otherwise desired.
It would therefore be desirable to develop a CR scanning technique that enables complete and efficient energy collection from the CR plate. In addition, it would be desirable to develop a CR scanning technique that is capable of collecting both prompt and stored emission from a CR plate during an X-ray exposure. It is also desirable to create a system with no moving parts to avoid damage to the imaging plates and to result in an easily maintained device.